1. Field of the Invention
The present invention relates to the field of semiconductor Integrated Circuits (ICs); more particularly, the invention relates to voltage regulators integrated in chips of semiconductor material.
2. Discussion of the Related Art
ICs can be classified in two broad categories, depending on the magnitude of the voltage differences that occur across the terminals of the electronic components included therein.
More specifically, in ICs belonging to a first category, from now on called “low-voltage ICs”, all the electronic components can only withstand (without malfunctioning or breaking thereof voltage differences between their terminals that are limited by a relatively low value—typically equal to the IC power supply voltage (such as 1.8V-3V). For example, those electronic components are low-voltage MOSFETs, which may be subjected to gate oxide breaking or undesired junction's breakdown when voltages exceeding the supply voltage are applied to their terminals (for example, between their gate terminal and any other terminal thereof.
The ICs belonging to a second category, from now on called “high-voltage ICs”, instead include electronic components that guarantee the capability of withstanding, at least between a pair of their terminals, higher voltage differences (such as up to 12-14V). For example, those components may be high-voltage MOSFETs, which are designed in such a way to avoid the occurrence of gate oxide breaking or undesired junction's breakdown even when high voltages exceeding the supply voltage are applied to their terminals.
For example, high-voltage ICs are common in the field of memory devices, and especially in non-volatile memories; indeed, in this case high-voltages are generally used to modify the stored data (e.g., to program and/or erase selected memory cells), so that the corresponding circuitry should be implemented with high-voltage components.
The high voltages needed by the non-volatile memories may be provided from the outside, or—more advantageously—they are generated directly on chip. In the latter case, the generation of the high voltages is accomplished by dedicated boosting circuits, like charge pumps, which are capable of generating voltages higher than the IC supply voltage—starting from it. Typically, such boosting circuits are coupled to a voltage regulator, which is used to stabilize the high voltage thus obtained (so as to reduce any possible variation of its value from the desired one). Moreover, the voltage regulator is generally able to modulate the (stabilized) high voltage that is output so making available different values thereof (at most equal to the high voltage received from the boosting circuit). Since the voltage regulator manages the above-mentioned high voltages, it should be implemented with high-voltage components (such as high-voltage MOSFETs).
Generally, the high-voltage MOSFETs have a gate oxide layer thicker than that used for the low-voltage MOSFETs. Indeed, the thicker the gate oxide layer the higher the voltage withstood at the terminals of the MOSFETs (without any undesired breaking). Since the high-voltage MOSFETs occupy more silicon area than the low-voltage MOSFETs, the voltage regulator wastes a significant area of a chip wherein the non-volatile memory is integrated.
Moreover, the non-volatile memory manages low-voltages as well (for example, in its control circuits). For this reason, both low-voltage MOSFETs and high-voltage MOSFETs should be provided.
Such a requirement increases the number of processing steps and masks (for example, for differentiating the oxide thickness of the low-voltage and high-voltage MOSFETs); this has a detrimental impact on the manufacturing process of the non-volatile memory.